1. Field of the Invention
This invention relates to a method and apparatus for automated dispensing of liquid materials through a flexible nozzle in contact with a workpiece.
2. Description of the Related Art
Automated dispensing of liquid materials such as adhesives, coatings, sealers and the like onto a workpiece may be accomplished by a three-axis programmable dispensing system having a movable arm and a needle carried by the arm for discharging liquid materials onto a workpiece. Systems of this type are often programmed to discharge the liquid materials along a straight or curved path at one or more locations on the workpiece. Microcomputer controlled stepper motors or linear motor drives provide precise control for the arm so that the needle can be accurately moved and positioned.
The needle of many conventional dispensing systems is made from an elongated, rigid, metal tube and has an outlet at one end thereof for discharging the liquid materials. However, if the needle contacts a portion of the workpiece or a support carrying the workpiece, the needle may bend or kink. As a consequence, much effort has been directed in the past to carefully program the microcomputer controlling the movement of the arm so that the outlet of the needle is always spaced a slight distance from the workpiece and contact with the workpiece or the support is avoided. The programming task becomes somewhat complex if, for instance, the workpiece is formed with a number of irregular, contoured or curved surfaces.
Other needles used in automated dispensing systems are made from a plastic such as Teflon or polypropylene in order to avoid a reaction between the needle and certain materials being dispensed. Although plastic needles are somewhat flexible, such needles tend to become limp when hot and may curl when cool, and as a result the outlet of the needle may miss its intended location as the needle moves along its programmed path. In addition, the plastic needle may kink if bent excessively which may interrupt further dispensing of the materials. In some instances, a rigid metal sleeve has been provided to surround the plastic needle along an upper portion of its length, but the sleeve may be permanently deformed if the sleeve unintentionally contacts the workpiece or the support for the workpiece.